Method and apparatus for gaseous mixing in a diesel exhaust system

ABSTRACT

A mixing device and method for a diesel exhaust system is disclosed having a chamber, a mixer within the chamber, and an injection tube supported on the mixer within the chamber. The mixer is positioned within the chamber adjacent an inlet and includes a plurality of angled blades to effect turbulent flow in a diesel exhaust stream entering the chamber through the inlet. The injection tube includes a plurality of injection points (e.g., openings) for discharging a reagent, such as gaseous ammonia (NH 3 ), into the exhaust stream. The injection tube is curved, and more specifically it is coiled with the injection points spread along the length of the tube in order to deliver reagent across a section of the chamber perpendicular to the exhaust stream flow.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to an apparatus and method for treatingand mixing diesel exhaust in a diesel exhaust system. Particularly, thepresent invention provides methods and apparatus for injecting reagentinto a diesel exhaust stream to reduce nitrogen oxides (NO_(x)) withoutincreasing the packing space of the exhaust system.

BACKGROUND OF THE INVENTION

Diesel engines are efficient, durable and economical. Diesel exhaust,however, can harm both the environment and people. To reduce this harm,governments, such as the United States and the European Union, haveproposed stricter diesel exhaust emission regulations. Theseenvironmental regulations require diesel engines to meet the samepollution emission standards as gasoline engines.

Typically, to meet such regulations and standards, systems requireequipment additions and modifications. Additional equipment can oftenlead to additional weight and/or additional packaging length.

For example, a lean burning engine provides improved fuel efficiency byoperating with an amount of oxygen in excess of the amount necessary forcomplete combustion of the fuel. Such engines are said to run “lean” oron a “lean mixture.” However, the increase in fuel efficiency is offsetby the creation of undesirable pollution emissions in the form ofnitrogen oxides (NO_(x)). One method used to reduce NO_(x) emissionsfrom lean burn internal combustion engines is known as selectivecatalytic reduction. When used to reduce NO_(x) emissions from a dieselengine, selective catalytic reduction involves injecting atomized ureainto the exhaust stream of the engine in relation to one or moreselected engine operational parameters and running the stream through areactor containing a catalyst. However, selective catalytic reductionand the use of aqueous urea involve many disadvantages, including addedpackaging weight and added packaging length to the exhaust system, aswell as the highly corrosiveness and poor lubricity of aqueous urea.

It would be advantageous to provide methods and apparatus for addressingthe regulations and standards without adding weight or length to analready complex diesel exhaust system. Accordingly, it would beadvantageous to provide methods and apparatus for injecting a NO_(x)reducing reagent into the diesel exhaust stream of a lean burn enginewhere little or no added weight or packaging length is required.Further, it would be advantageous to provide a mixing system whichcreates a more homogenous mixture in a limited length. It would also beadvantageous to provide an injector which is capable of distributing thereagent more uniformly throughout a cross-section of the treatment area.Accordingly, it would be advantageous to provide multiple injectionpoints within a diesel exhaust stream.

The methods and apparatus of the present invention provide the foregoingand other advantages.

SUMMARY OF THE INVENTION

There is disclosed herein an improved diesel exhaust treatment systemand method which avoid disadvantages of prior devices and methods, whileaffording additional structural and operating advantages.

Generally speaking, a mixing device for a diesel exhaust system isdisclosed having a chamber, a mixer within the chamber, and an injectiontube supported on the mixer within the chamber. The mixer is positionedwithin the chamber adjacent an inlet and includes a plurality of angledblades to effect turbulent flow in a diesel exhaust stream entering thechamber through the inlet.

In specific embodiments of the system, the injection tube includes aplurality of injection points (e.g., openings) for discharging a reagentinto the exhaust stream. The injection tube is curved, and morespecifically it is coiled with the injection points spread along thelength of the tube in order to deliver reagent across a section of thechamber perpendicular to the exhaust stream flow.

The disclosed method for mixing gaseous ammonia in a diesel exhaustsystem begins with a diesel exhaust stream from a diesel engine passingfrom the engine through a conduit in fluid communication with theengine. The exhaust stream is directed to flow through the conduit intoa housing having a mixer, an injection tube and an exit disposedtherein. Turbulent flow in the diesel exhaust stream is created withinthe housing as the stream passes through the mixer. A continuousinjection of gaseous NH₃ from the injection tube into the diesel exhauststream is made as the stream moves from the mixer toward the housingexit to create a treated homogenous exhaust stream. Finally, the treatedexhaust stream is discharged through the housing exit.

These and other aspects of the invention may be understood more readilyfrom the following description and the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For the purpose of facilitating an understanding of the subject mattersought to be protected, there are illustrated in the accompanyingdrawings embodiments thereof, from an inspection of which, whenconsidered in connection with the following description, the subjectmatter sought to be protected, its construction and operation, and manyof its advantages should be readily understood and appreciated.

FIG. 1 is a schematic illustrating a typical mixer/injector device in adiesel exhaust system;

FIG. 2 is a schematic illustrating an embodiment of a mixer/NH₃injection device of the present invention in a diesel exhaust system;

FIG. 3 is a schematic illustrating another embodiment of a mixer/NH₃injection device of the present invention in a diesel exhaust system;

FIG. 4 is a front view of an embodiment of a mixer/NH₃ injection device;and

FIG. 5 is a perspective view of the mixer/NH₃ injection device of FIG.4.

DETAILED DESCRIPTION OF THE INVENTION

While this invention is susceptible of embodiments in many differentforms, there is shown in the drawings and will herein be described indetail a preferred embodiment of the invention with the understandingthat the present disclosure is to be considered as an exemplification ofthe principles of the invention and is not intended to limit the broadaspect of the invention to embodiments illustrated.

Referring to FIG. 1, there is illustrated a typical mixer/injectordevice. Exhaust is discharged from the diesel engine 100, throughconduit such as exhaust piping to an exhaust treatment system 110. Theexhaust treatment system 110 typically consists of, in downstream order,a diesel oxidation catalyst (DOC) 112, a diesel particulate filter (DPF)114, a mixer/NH₃ treatment canister 116, and a NO_(x) slip catalyst(NSC) 118. The DOC 112, DPF 114 and NSC 118 are additional exhausttreatment structures present in most diesel exhaust treatment systemsand which form no part of the present system 10. Such structures will begenerally referenced herein and identified in the drawing figures but,as each of these additional exhaust treatment structures is commonlyunderstood by those skilled in the art, a detailed discussion of each isavoided for the purpose of focusing discussion on the system 10 as setforth in the appended claims.

The mixer/treatment canister 116 is shown to include a connection pipe120 with an injector 122 at the upstream end where NH₃—or an NH₃containing reagent—is injected into a laminar diesel exhaust flow as itis discharged from the DOC 112 and DPF 114. The ammonia/exhaust streamthen passes through a mixer 124 to effect mixing of the NH₃ and thediesel exhaust. A substantial length of pipe 120 is needed to allow foradequate mixing of the two components before the flow enters the NSC118. As such, the mixer/injector system adds packaging length and weightto the diesel exhaust system 100 which might otherwise be used for otherafter-treatment substrates.

Referring to FIGS. 2-5, there is illustrated a mixer/NH₃ injectionsystem, generally designated by the numeral 10. The system 10 is shownin two distinct exhaust treatment configurations. FIG. 2 illustrates aconfiguration similar to that of FIG. 1 where the downstream order ofcomponents is DOC 12, then DPF 14 and NSC 18 sandwiched about system 10.Alternatively, FIG. 3 illustrates a configuration where the NSC 18 is onthe DPF 14—i.e., NO_(x) slip catalyst on diesel particulate filter (NPF)19—sandwiching the system 10 with the DOC 12. Other configurations mayexist in which the system 10 is moved up or downstream in the exhaustflow.

Regardless of the specific configuration, it is clear from examinationof FIGS. 2 and 3 that the packaging space required for system 10 issubstantially reduced from that required for a typical mixer/injectordevice 110 illustrated in FIG. 1.

Generally speaking, system 10 is comprised of a housing 20 defining amixing chamber 25, an injection tube 22 fed by an exterior injector boss30 coupled to a supply (not shown), and a mixer 24. FIGS. 2 and 3illustrate the diameter of the housing 20 (approx. 12 inches (30.5 cm))is substantially equal to that of the surrounding structures—e.g., DPF14 and NSC 18. By providing the larger diameter system housing 20 (vs.narrow connecting pipe 120), the need for reducers 123 (FIG. 1) iseliminated, further reducing the packaging size of the entire dieselexhaust treatment system.

FIGS. 4 and 5 illustrate a specific embodiment of a single-plane, coiledinjection tube 22. Injection tube 22 enters through the housing sidewalland begins a tortuous path to a center of the chamber 25. The tube 22includes a series of injection points 23 where reagent can be emittedinto the chamber 25. The injection points 23 are spaced along the tube22 and, therefore, throughout a cross-section of the chamber 25 toprovide a more uniform distribution of reagent throughout thatcross-section of the mixing chamber 25. The uniform distribution intothe exhaust stream results in a more homogenous mixture of reagent andexhaust in a shorter mixing period.

The tube 22 may be configured in several alternative shapes, includingcircular and serpentine, so long as a distribution of the injectionpoints 23 throughout a cross-section of the chamber is provided.Further, the injection points 23 comprise small openings in the tube 22to allow discharge of the reagent from the tube 22. To effect a uniformor even discharge from all the injection points 23, the first openinghas a very small diameter and successive opening diameters increasetoward the tube end 27—i.e., the smallest diameter openings arepositioned at the beginning of the tube where the fluid pressure is thegreatest. The purpose, again, is to achieve even distribution of reagentacross the entire cross-section of the mixing chamber 25.

Also shown in FIGS. 4 and 5, is exhaust flow mixer 24. The mixer 24 iscomprised of a plurality of fixed blades 37, four are shown, secured toone another at a midpoint and outwardly to and within a short section(approx. six inches (15.2 cm)) of the housing 20. The blades 37 areangled from back to front as a way of imparting a turbulent flow to thesubstantially laminar exhaust flow entering system 10. Though not shown,additional blade configurations are possible to achieve the desiredturbulent exhaust flow for mixing.

Another feature of the mixer 24 is that it supports the injection tube22. That is, the tube 22, which is positioned on the downstream side ofthe mixer 24, attaches to, by way of welds or any other suitableattachment means, each of the mixer blades 37 for simple structuralsupport. Attachment may be achieved, for example, at the areas 39 wherethe tube 22 crosses each blade 37. The securing of the coiled tube 22alleviates damage which might otherwise be caused by the more violentvibration of the tube 22 during operation of the vehicle. Reagent (e.g.,gaseous NH₃) discharged from injection points 23 immediately enters theturbulent diesel exhaust stream as it moves toward the chamber exit 35(FIGS. 2 and 3). A relatively short distance is needed to provide thenecessary mixing time to create a homogonous reagent/diesel exhaust.

The homogenous mixture is then exited from the mixing chamber 25 intoone of either the NSC 18 (FIG. 2) or the NPF 19 (FIG. 3) for furthertreatment.

The matter set forth in the foregoing description and accompanyingdrawings is offered by way of illustration only and not as a limitation.While particular embodiments have been shown and described, it will beapparent to those skilled in the art that changes and modifications maybe made without departing from the broader aspects of applicants'contribution. The actual scope of the protection sought is intended tobe defined in the following claims when viewed in their properperspective based on the prior art.

1. A mixing device for a diesel exhaust system comprising: a chamberhaving an inlet at one end for permitting entrance of an exhaust streamfrom a diesel engine and an outlet at an opposing end; a mixer withinthe chamber adjacent the inlet and positioned to effect turbulent flowin an exhaust stream entering the chamber through the inlet; and aninjection tube supported within the chamber by the mixer.
 2. The mixingdevice of claim 1, wherein the injection tube comprises a plurality ofinjection points therein for discharging a reagent into the exhauststream, and extends within a plane of the chamber.
 3. The mixing deviceof claim 2, wherein the injection tube is curved.
 4. The mixing deviceof claim 2, wherein the injection tube is coiled.
 5. The mixing deviceof claim 1, wherein the mixer comprises a plurality of fixed bladesangled to deflect the exhaust stream.
 6. The mixing device of claim 2,wherein the mixer comprises a plurality of blades angled to impartmixing to the exhaust stream and the injection tube extends across eachblade within the chamber.
 7. The mixing device of claim 1, wherein theinjection tube is connected to the mixer.
 8. The mixing device of claim1, wherein the chamber is positioned between a diesel particulate filter(DPF) and a NO_(x) slip catalyst canister.
 9. The mixing device of claim1, wherein the chamber is positioned between a diesel oxidation catalyst(DOC) canister and a NO_(x) particulate filter (NPF) canister.
 10. Amixing device for a diesel exhaust system comprising: a chamber havingan inlet at one end for permitting entrance of an exhaust stream from adiesel engine and an outlet at an opposing end; a mixer within thechamber adjacent the inlet; and an injection tube having a plurality ofinjection points and extending into the chamber.
 11. The mixing deviceof claim 10, wherein the injection tube is supported by the mixer withinthe chamber.
 12. The mixing device of claim 10, wherein the injectiontube is curved.
 13. The mixing device of claim 12, wherein the injectiontube is coiled.
 14. The mixing device of claim 10, wherein the mixercomprises a plurality of fixed blades angled to effect turbulent flow inthe exhaust stream.
 15. The mixing device of claim 11, wherein the mixercomprises a plurality of blades angled to impart mixing to the exhauststream and the injection tube extends across each blade within thechamber.
 16. The mixing device of claim 10, wherein the injection tubeis connected to the mixer.
 17. The mixing device of claim 10, whereinthe chamber is positioned between a diesel particulate filter (DPF) anda NO_(x) slip catalyst canister.
 18. The mixing device of claim 10,wherein the chamber is positioned between a diesel oxidation catalyst(DOC) canister and a NO_(x) particulate filter (NPF) canister.
 19. Amethod for mixing gaseous ammonia in a diesel exhaust system comprisingthe steps of: a. exhausting a diesel exhaust stream from an enginethrough a conduit in fluid communication with the engine; b. directingthe diesel exhaust stream to flow through the conduit into a housinghaving a mixer, an injection tube and an exit disposed therein; c.creating a turbulent flow in the diesel exhaust stream within thehousing as the stream passes through the mixer; d. injecting gaseous NH₃from the injection tube into the diesel exhaust stream as the streammoves from the mixer toward the housing exit to create a treated exhauststream; and e. discharging the treated exhaust stream through thehousing exit.
 20. The method of claim 19, wherein the mixer comprises aplurality of fixed blades angled to deflect the diesel exhaust stream.21. The method of claim 19, wherein the injection tube comprises aplurality of injection points for introducing NH₃ gas into the dieselexhaust stream.
 22. The method of claim 21, wherein the injection tubeis supported in the housing by the mixer.
 23. The method of claim 21,wherein the injection tube comprises a coil.
 24. The method of claim 19,further comprising the step of creating a homogenous mixture of dieselexhaust and gaseous NH₃.
 25. The method of claim 24, wherein the step ofcreating a homogenous mixture comprises the step of injecting gaseousNH₃ into the diesel exhaust stream at a plurality of points.
 26. Themethod of claim 25, wherein the injection tube comprises a plurality ofinjection points spaced throughout a cross-section of the housing.
 27. Amethod of treating diesel exhaust from an engine in a motor vehicle, themethod comprising the steps of: a. exhausting a diesel exhaust streamfrom an engine through a conduit in fluid communication with the engine;b. directing the diesel exhaust stream to flow through the conduit intoa housing having a mixer, an injection tube and an exit disposedtherein, wherein the injection tube is in fluid communication with areagent supply; c. creating a turbulent flow in the diesel exhauststream within the housing as the stream passes through the mixer; d.injecting a gaseous reagent from the reagent supply through theinjection tube into the diesel exhaust stream as the stream moves fromthe mixer toward the housing exit to create a treated exhaust stream;and e. discharging the treated exhaust stream through the housing exit.